Seeking TIG Feedback

[metros]

Hello All,
Looking for some feedback on my newb TIG tack welds. I've played around and watched many youtube videos. My exhaust is the only thing holding me back from registering and enjoying it this summer. I've decided that I need to spend considerably more time to get my skills to the point where I can TIG my exhaust. I have opted to instead tack everything where I want it to be and then have my local shop finish weld everything.

I'm looking for feedback from those that have experience under their belts. If I brought this into your shop would you be willing to finish weld this? Any other feedback is appreciated as well.

Everything is 304 stainless. Not using filler rod to tack as it doesn't seem necessary. The only thing to note on this piece is that the bellmouth was oval shaped and this was my attempt to transition it to 3" round for the rest of the exhaust. I used these two pieces of stainless and squished them in a bench vice to transition from oval to round. So they don't line up perfectly, but they're as close as I could get them. Using a bench sander to clean up the surfaces prior to welding. Alphastar Tig, 103 amps, pulse set to 100pps.

My thought is that I spent a little too long on each one, which meant they got a bit more heat than I should shoot for. What else?

https://i.imgur.com/ZkXXrdA.jpg

https://i.imgur.com/H9D6YaU.jpg

https://i.imgur.com/xoOzhoH.jpg

https://i.imgur.com/NTpDZG2.jpg

[NAZ]

The weld to the flange looks good from this angle. The tacks also look good from the photos. Take the time to fit the gaps much closer, especially on thin SS -- SS tends to warp much more than mild steel. Now the real trick with pipe welding (or tubing in this case) is to make a bead on the inside while welding on the outside.

Another trick especially with SS is to use shielding gas on the inside. If not, you may find the base metal won't fuse together properly and you'll see lots of carbon precipitation and scale on the surface. When it comes to welding the area you're welding must be very clean. You're basically casting metal when you lay a bead and any impurities that get in the puddle will degrade the weld.

I'd let you weld my exhaust.

[Mike N]

Looks Iike a turbo flange. If I was welding a part in such a high stress and hot location I would definitely back purge the welds. The 'sugaring' you will get on the inside of the welds will cause a crack or weld failure at some later time. Back purging is probably overkill for downstream exhaust welds but for something like that I would definitely make the effort.

[metros]

I'm aware of backpurging but didn't think it was necessary for just the tack welds. Are you guys recommending I back purge the tack welds in addition to final welds?

[metros]

Next question: I'll have a cat in the exhaust system. I'd like to big-band the cat in. The cat and v-bsnd are pictured below. Tips for tracking this in place? The material is much thicker on both sides, but still 304 stainless. Should I turn the amps up another 30 given the additional thickness? I don't have any practice pieces to trial before the real deal so I'm a bit more apprehensive.

https://i.imgur.com/8xv2vlu.jpg

[NAZ]

Depends. In welding school you're taught the best way to make perfect welds. Then when you start working in the field you learn from the gray haired welders what short cuts you can get away with. If you need a perfect x-ray quality weld on SS pipe that means 100% penetration and you will be back purging even the tack welds. Any scaling on the tack welds has to be removed. When I welded structural I usually had access to both sides or in many cases I was able to use backing plates. When I welded pipe you don't have access to the inside but the inspector can see where you can't reach so your tack welds must be perfect or they will leave a defect in your weld.

Now, for a set of headers -- myself, I don't worry about perfect 100% penetration. It's not a life safety system. No need to turn a simple job into a complicate project. I also typically don't choose SS for headers I have to work around. They take forever to cool and I've been burned enough over my years of welding for a living. But if you like using SS purchase the low carbon variety, usually indicated by an "L" after the alloy, i.e. 316L.

For dissimilar thickness metals you need to increase the amps enough to melt the thicker material and concentrate the torch angle toward the thicker material. Get some scraps to practice on and get your settings just right before attempting the weld.

[STiPWRD]

The v-band flange doesn't have to be clocked a certain way, so does it need to be tacked on? Why not let the weld shop handle it? Btw, that's awesome that you got a tig welder!

Let me know if you want to borrow my OEM wrx down pipe to pass emissions, that cat should still be good.

[metros]

If I don't tack it all together start to finish then the end point could be off from where I want it to be.

I'm hoping to not need the OEM downpipe. Think I've got a guy that will jump me through that hoop.

[Mike N]

No need for back purging for tack welds for automotive applications. If you don't want the hassle or expense of back purging you can get some of the benefits by using a flux such as Solar B. It's not going to give you the same results as back purging but if you limit the weld bead penetration it works well.

[Jacob McCrea]

"Tips for tacking this in place?"

I've been able to control warpage reasonably well, with both mig and tig, by tacking tubing at 12 o'clock, then 6 o'clock, then 9 o'clock, then 3 o'clock, so to speak. And as noted above, having the gap as tight as possible, which further prevents warpage.

[Zach34]

I'd be a little worried about not back-purging those tacks, as hot as they were. Take a look inside the pipe, if the back-side of the tack looks like a charcoal crumb, you will have to clean/grind it. The charcoal-looking stuff is oxidation and will get pulled into the final weld and contaminate it.

Other minor things:

You'd be doing the final welder a favor if you evenly space the tacks as much as possible. I realize you probably placed a few extra to force the fit-up into place.

Those small gaps in the second picture, and especially the large one in the third picture, will make it extremely challenging to get a cosmetically good-looking weld. Sometimes there's just not much you can do, but those gaps have to be bridged with more filler rod than you might expect which means more heat and slower puddle movement. Even that little lip on the left of the first picture will affect the puddle flow and change the look of the weld in that spot.

The parts will still move around after final welding. Stainless moves/expands/contracts like you wouldn't believe. If you don't have much tolerance for fit-up, let the welder know and he can make small stitches and go slower to minimize the movement.

You did well tacking without filler, but those few spots where there was a small gap probably could have been tacked faster and with less heat if you used just a tiny bit of filler - maybe even one size smaller rod than you would use for final welding.

Overall good job! Stainless can be very frustrating to get a good-looking weld. I'm far from mastering it.

[metros]

Thanks for the input all.

Those gaps on the pieces are from the abrasive wheel I'm using to cut with. I'm looking at getting a blade for my chop saw instead of continuing to use the abrasive wheel. Those divots in the otherwise perfectly flat plane of the cuts are either the start or end of the cut through process with the wheel.

Wish I had known there were chop saw specifically for cutting metal with. They're much cheaper than the chop saw I actually ended up purchasing. Mine is made for wood really but has a lot of nice features for future construction projects around the house. Trying to get the best of both worlds.

[metros]

A few more recent tack welds. The more time and experience I get behind the torch the easier things go. Would still benefit from getting lots more hours of practice.

https://i.imgur.com/x94TPnB.jpg

[Zach34]

Looks good!

That is a good idea to have it clamped while welding, if possible. I had a v-band flange warp considerably on me during final welding, probably due to imperfect fit-up against the tube. A little work on a wide belt sander and I was able to salvage it, though, so it wasn't too extreme.